Development of fetal gyri, sulci and fissures: a transvaginal sonographic study.

We aimed to determine the feasibility of imaging specific sulci, gyri and fissures using transvaginal sonography and to correlate their first sonographic recognition with gestational age. Retrospectively, 262 fetal brain scans were analyzed from a total of 337 scans. Scans were selected if any of the following structures were seen: in the coronal plane the lateral, callosal and cingulate sulcus and gyrus; in the median plane the parieto-occipital and calcarine fissures, and the cingulate gyrus and sulcus; and, in an oblique section, the lateral sulcus. The gestational age at which the fissures, sulci and gyri were first imaged was recorded and subsequently compared with similar anatomical studies from the literature. It was possible to identify all the targeted structures. The gestational ages at which the structures were first imaged were: the callosal sulcus, from 14 weeks; the lateral sulcus, from 18 weeks; the parieto-occipital sulcus and calcarine fissure, from 18 weeks; and the cingulate gyrus, from 26 weeks. We concluded that the developmental maturation of the normal fetal brain follows a predictable timetable, and that this maturation can be grossly followed with sonography. The sonographic recognition of the fissures, gyri and sulci lagged behind the observations by anatomical studies. The greatest discrepancy was the first appearance of the cingulate gyrus which, in the anatomical studies, could be seen by 18 postmenstrual weeks and, in our study, was seen after 26 postmenstrual weeks. The one exception was the callosal sulcus, which was first seen at 14 postmenstrual weeks in both the sonographic and anatomical studies. In conclusion, the recognition of specific structures of the cortical map is possible. Sonography may be used to image the developing cortical surface.